Apparatus and method for forming oxygen-enriched gas and compression thereof for high-pressure mobile storage utilization

ABSTRACT

An oxygen concentrator is utilized in combination with a compressor to provide a highly enriched and compressed oxygen gas in a mobile container such as a gas cylinder. The combination and method of production provides for the facile preparation of an enriched source of oxygen for use by an ambulatory or wheelchair-confined patient. The oxygen concentrator utilizes two or more molecular sieves to provide a breathable gas of from approximately 80 to about 98 percent oxygen from atmospheric air. The oxygen-enriched gas is stored in a concentrator product tank and can be prioritized so as to supply a patient with a proper amount and concentration of oxygen and secondarily to supply any surplus or excess enriched oxygen to a compressor. The compressor utilizes multiple stages to produce the highly compressed oxygen-enriched gas and utilizes a two-part piston at low rpm to enhance low wear and low noise. The multiple pistons of the compressor can either all rotate at one RPM or in an alternative embodiment, at least a first piston can rotate at a higher RPM than any remaining pistons. Desirably, at least the initial piston of the alternative embodiment is driven by one drive shaft source with one or more other remaining pistons being driven by a second drive shaft.

CROSS-REFERENCE

This application is a continuation-in-part of U.S. Ser. No. 08/942,063,filed Oct. 1, 1997 for an Apparatus and Method for FormingOxygen-Enriched Gas and Compression Thereof for High Pressure MobileStorage Utilization now U.S. Pat. No. 5,988,165.”

FIELD OF INVENTION

The present invention relates to an apparatus and process for producingenriched oxygen which is subsequently collected under high pressure in aportable container for ambulatory patient use and to permit facilepatient mobility. A compressor can have all the pistons thereof operatedby a single drive shaft, or an alternative, compact compressor canutilize at least two different drive shafts having at least one pistonreciprocating at a higher RPM than one or more of the remaining pistons.

BACKGROUND OF THE INVENTION

Heretofore, oxygen concentrators have been utilized to supply patientswith a gas having a high oxygen concentration for extended periods oftime. Oxygen concentrators typically produce a breathable gas containingfrom about 80 present to about 96 present oxygen from atmospheric airand thus have been widely utilized in the home health care field.

U.S. Pat. No. 4,627,860, to Rowland, relates to a microprocessor andcooperating means for monitoring or sensing functions and performance ofvarious components of the concentrator. A test apparatus having meansfor selecting any of the functions monitored by the microprocessor isconnected to the concentrator and displays the selected monitoredfunctions for diagnosing performance levels and component problems orfailures.

U.S. Pat. No. 5,071,453, to Hiradek et al. relates to an oxygenconcentrator which is intended for aircraft use. A booster compressor isused to increase the pressure of the product gas from the concentratorin order to increase the amount of the gas which can be stored in aplenum. The booster includes two moving pistons which are rigidly linkedtogether and a series of check valves which control the flow of gasesthrough the compressor. One of the pistons is driven by air from therotary valve in the concentrator, and the other piston compresses theproduct gas for delivery to the plenum. A small sample of concentratorproduct gas is monitored by an oxygen sensor for oxygen concentration.Once the oxygen concentration has reached an acceptable level, thebooster compressor fills the plenum with product gas. Thereafter, if theoxygen concentration of product gas delivered to the crew from theconcentrator falls below the concentration which is required at aparticular altitude, the product gas stored in the plenum is deliveredto the crew. The oxygen sensor monitors the concentrator output productgas to the breathing regulator when the stored plenum gas is not beingused.

U.S. Pat. No. 5,354,361, to Coffield, relates to a pressure-swingadsorber system including a pneumatically driven booster compressor toincrease the pressure of the output product gas. A pair of inlet valvescontrols feed air flow to the sieve beds and the drive cylinder of thebooster compressor and are cycled so that one valve opens to pressurizeone sieve bed before the other valve closes to allow the other sieve bedto vent to atmosphere. During the time that both valves are open, thepressure in the two sieve beds and on opposite sides of the drivecylinder equalize and a portion of the gas in the pressurized sieve bedand drive cylinder side is captured rather than being vented to ambient.System efficiency is increased by selecting whether captured gas fromthe last pressurized sieve bed or drive cylinder side reaches the nextto be pressurized sieve bed first.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a method andapparatus for storing high-pressure, high-purity oxygen in a pressurevessel for use in the home health care or related fields as forambulatory patients, persons confined to wheelchairs, and those who arebedridden.

In accordance with the invention there is provided a method andapparatus for producing from air an oxygen-enriched gas and initiallystoring the same in a concentrator product tank. Desirably butsecondarily, at least a portion of the oxygen-enriched gas is fed bydifferent methods to a compressor buffer tank where it is stored. Afterreaching a predetermined pressure, the gas is fed to a compressor whereit is compressed to a high pressure and stored in a mobile or portablehigh-pressure container. This eliminates the requirement of an oxygenconcentrator which contains a first compressor and requires connectionto an electrical outlet. A patient can thus have increased mobilitythrough use of the portable, high-pressure oxygen container.

It is a further aspect of the invention to provide electrical circuitryto assure prioritization of the flow rate and concentration of theenriched gas to a patient.

The excess gas, when available, is simultaneously delivered to anindependent, multi-stage compressor.

In accordance with another aspect of the invention there is provided ahome health care oxygen concentrator for physically separating moleculesof oxygen from air with oxygen in a subsequent operation being fed to ahigh-pressure vessel. The concentrator comprises one or more molecularsieve beds containing a physical separation material, a first (i.e.,feed stock) compressor to provide a feed source of compressed air,control means which regulate the product gas flow through the beds to aconcentrator product tank, a second enriched-gas storage tank (i.e., abuffer tank), and a second compressor, e.g., multi-stage, which is notoperated by the first compressor but operates independently thereof andenables the oxygen-enriched gas to be compressed and fed to ahigh-pressure vessel or container. The second compressor has a two-partpiston assembly which results in low wear. In an alternative embodiment,a compressor can be utilized which has a variety of features such as afirst stage wobble piston connected to a first drive shaft, one or moresubsequent pistons sequentially aligned to increase the pressure of agas with such pistons being connected to a second drive shaft, and ableed-off valve which serves to abate noise when the compressor isdisconnected from the high pressure vessel. The alternative compressoris compact, lightweight, and cost efficient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an oxygen concentrator for separatingoxygen from a gaseous mixture such as air;

FIG. 2 is a block diagram of an apparatus and process in accordance withthe present invention for compressing oxygen-enriched air and feeding itto a portable container;

FIG. 3 is a block diagram of the apparatus and process of the presentinvention for feeding a portion of enriched gas at a controlled rate toa patient and another portion of the enriched gas to a compressor forhigh-pressure storage in a portable container;

FIG. 4 is a block diagram of the apparatus and process of anotherembodiment of the present invention for feeding a portion of enrichedgas at a controlled rate to a patient and another portion of theenriched gas to a compressor for high-pressure storage in a portablecontainer;

FIG. 5 is a schematic showing one portion of a control circuit foroperating a multiple-stage compressor of the present invention;

FIG. 6 is a schematic of the remaining portion of the control circuit ofFIG. 5 for operating a multiple-stage compressor of the presentinvention;

FIG. 7 is a side elevational view of the compression apparatus of thepresent invention;

FIG. 8 is a top plan view of the compression apparatus of the presentinvention;

FIG. 9 is a side elevational view of the upper portion of the two-partpiston assembly of the present invention;

FIG. 10 is a side elevational view of the bottom portion of the two-partpiston assembly of the present invention.

FIG. 11 is a top plan view of an alternate embodiment compressorapparatus of the present invention;

FIG. 12 is a front elevational view of the alternative compressionapparatus shown in FIG. 11;

FIG. 13 is a rear elevation view of the alternative compressionapparatus shown in FIG. 11;

FIG. 14A is a partial plan view of a first piston of the presentinvention;

FIG. 14B is an enlarged partial elevation view of the second piston ofthe present invention;

FIG. 14C is an enlarged partial elevation view of the third piston ofthe present invention; and,

FIG. 15 is an electrical schematic of the various circuits forcontrolling the compact compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While a preferred embodiment of the invention is described hereinbelow,it is to be understood that the various aspects and parameters of thepresent invention can vary and be different such as the pressure andpurity of the oxygen-enriched gas exiting from a concentration producttank, the pressure at which the enriched gas is fed to the patient andits flow rate, the pressure maintained in a buffer tank, the pressure atwhich the compressor initially draws enriched gas from the buffer tank,the buffer tank pressure at which the compressor shuts off, and thelike. Moreover, while reference is made to a particular oxygenconcentrator as set forth immediately below, generally any type ofoxygen concentrator can be utilized which yields a source of enrichedair containing anywhere from about 50 percent oxygen up to about 99percent by volume.

With reference to FIG. 1, the apparatus includes one or more, andpreferably two beds 10 and 12 which contain a physical separation mediumor material. The separation material selectively adsorbs one or moreadsorbable components as from air and passes one or more nonadsorbablecomponents of such a gaseous mixture. The physical separation materialcan be a molecular sieve with pores of uniform size and essentially thesame molecular dimensions. These pores selectively adsorb molecules inaccordance with molecular shape, polarity, degree of saturation, and thelike. In the preferred embodiment, the physical separation medium is analuminasilicate composition with 4 to 5 A (Angstrom) pores. Morespecifically, the molecular sieve is a sodium or calcium form ofaluminasilicate, such as type 5A zeolite. Alternately, thealuminasilicate may have a higher silicon-to-aluminum ratio, largerpores, and an affinity for polar molecules, e.g., type 13x zeolite. Thezeolite adsorbs nitrogen, carbon monoxide, carbon dioxide, water vapor,and other significant components of air.

A cross-over valving means 20, which preferably includes a four-wayvalve 21, selectively and cyclically connects the inlet end of two beds,one at a time, during a production phase with a source of the gasmixture, e.g., air under pressure supplied from a first compressor 22(i.e., the feed compressor), while the other bed is vented to atmosphereduring a purge phase. Specific to the preferred embodiment, thecross-over valving means selectively connects one of the beds in fluidcommunication with an air pump or compressor 22 which supplies air fromabout 15 to about 21 psi. As used herein, “fluid communication” refersto means allowing flow of the appropriate gases. Of course, vacuum canalso be used during the purge phase with the present invention toenhance evacuation. Compressor 22, which receives air from inlet 23, isconnected to a first drive motor 25, in the preferred embodiment about a¼ horsepower electric motor. A solenoid (not shown) or other cross-overvalve actuating means selectively causes the cross-over valving means tomove alternately between first and second positions. In the firstposition, the first bed 10 is connected with compressor 22 to causenitrogen adsorption and oxygen enrichment in the product gas, and thesecond bed 12 is vented to atmosphere to allow evacuation. In the secondposition, the first bed is vented to atmosphere to allow evacuation andthe second bed is connected with the air compressor to cause nitrogenadsorption. The invention is described with specific reference to apressure-swing control. However, it is equally applicable to othermethods of sequencing the gas flow through the sieve beds such as atiming-based system.

The composition of the gas in the voids of the zeolite varies fromsubstantially pure primary-product gas at the outlet end, to the ambientgaseous mixture composition at the inlet end. As the gas mixture isintroduced through a bed inlet to an adsorbed, gas-free or regeneratedbed, an adsorption zone of finite, relatively large size is formed. Thisadsorption zone is a region of the bed in which the fill capacity of theadsorbent to hold the adsorbable components has not been reached. Thisadsorption zone moves from the bed inlet toward a bed outlet with avelocity significantly less than the superficial gas velocity in thebed. When the adsorption zone reaches the outlet end of the bed,adsorbable components begin to flow through the bed outlet into thenonadsorbable primary product stream. This time is hereinafter referredto as the “breakthrough.” For a given gaseous composition, thebreakthrough is defined by the size and configuration of the bedcontainer as well as the packing configuration of the molecular sieveand the flow rate and bed gas pressure. The configuration of the bed isgenerally cylindrical and the output volume rate can vary from about 0.1to 6 liters per minute. The breakthrough is the time required for thediffusion reaction as the nitrogen saturates and is weakly bonded to thesieve bed. When breakthrough occurs, primary product-enriched bed gas inthe zeolite voids varies from a higher primary product gas concentrationat the bed outlet to a lower concentration at the bed inlet. In thepreferred embodiment, the primary product-enriched bed gas is about 80percent primary product at breakthrough. While adsorption is occurringin one bed, the adsorbable components adsorbed by the separation mediumof the other bed are purged from the other bed because of the drop inpressure due to atmospheric venting and because of exposure torelatively pure product gas from the first tank.

The first bed 10 is connected with a reservoir or product tank 30 by wayof a first check valve 32 or other unidirectional valving means. Thefirst check valve 32 permits the primary product gas from the first bed10 to flow into the reservoir or product tank 30 via line 46 when theproduct gas pressure in the first bed 10 exceeds the pressure of productgas in the reservoir or product tank 30. The first check valve prohibitsthe product gas from flowing from the reservoir or product tank 30 whenthe pressure in the first bed 10 is lower than the reservoir or producttank. More specific to the preferred embodiment, the check valve imposesa 1.5 psi bias such that flow is only permitted when the pressure in thefirst bed exceeds the pressure in the reservoir or product tank by 1.5psi. The second bed 12 is connected with the reservoir or product tank30 by way of a second check valve 34 or other unidirectional valvingmeans. The second check valve 34 again provides for unidirectional flowof the primary product gas from the second bed 12 to the reservoir orproduct tank 30.

A pressure equalization flow path 40 extends between outlets of thefirst and second beds. A concentration equalization valve 42 is eitheropen or closed to selectively permit or prevent gas flow through theflow path between the first and second beds. A control means 50cyclically causes the cross-over valve actuating means (i.e., twosolenoids) and the concentration equalization valve 42 to be operated.The control means periodically and cyclically enables a concentrationequalization valve actuator which is also a solenoid.

Oxygen sensor 43 registers the oxygen concentration of the product gasand can be located in the product tank 30. The sensor 43 communicates asensed value to the microprocessor (i.e., control means). Similarly, apressure sensor 45 registers the pressure in the product tank andcommunicates the same to the microprocessor.

The control means causes the cross-over valving means 20 to alternatebetween its first and second positions for the appropriate period duringeach cycle segment. A cycle segment can be either the product gasgeneration cycle or the purge cycle. The cycle duration is selected suchthat each bed is connected with the source of air for a period of timewhich is equal to or less than the breakthrough time. The mechanismwhich triggers the cross-over valving can be based on the pressure, suchas a pressure set point or set point range, in the bleed line from theproduct tank as is used in a pressure-based control cycle, or it can bebased strictly on a residence time from the product-producing bed, suchas in a timing cycle-based control cycle. In accordance with anotherembodiment of the invention, the control cycle can utilize variablepressure in order to achieve a residence time within a defined rangebased upon a projected breakthrough time. In the preferred embodiment,the beds are 3.5 inches in diameter, 15 inches in length, and eachcontains 6.5 pounds of 5A zeolite.

The gas mixture is supplied at up to 21 psi of pressure to the firstbed. Concurrently, the second bed (i.e., a “used” bed) is vented toatmosphere to cause purging of the nitrogen-enriched molecular sieves.Before the breakthrough time, the concentration equalization valve isopened allowing primary product-enriched gas from the first bed to flowinto the evacuated second bed. During the concentration equalizationperiod, one bed is evacuated and the other has just reached the pressureset point which drives flow between the beds. The flow is of high oxygencontent so that the first product to pass into the product tank via line46 is essentially product gas produced by the oxygen beds. The secondbed pressure is product-enriched gas to purge the sieve bed. Before theprimary product-enriched gas from the first bed is evacuated through thesecond bed, the cross-over valving means 20 is actuated to reverse itsposition. Actuating the cross-over valving means discontinues supplyingof the gaseous mixture to the first bed and commences evacuating it andconcurrently discontinues evacuating the second bed and commencessupplying it with the gaseous mixture.

Subsequent to the actuation of the cross-over valving means, theconcentration equalization valve 42 remains open to continue allowing apurge supply of product-enriched gas to flow into the second bed. Thisequalizes the concentration of gas which is supplied to the product tanksince the cycling is sequenced so that the product gas proceeds from thebreakthrough zone to flow into the product tank. Subsequently, theconcentration equalization valve closes and terminates the flow ofprimary-product gas between the beds. In the second segment of thecycle, the pressure in the second bed increases approaching the gasmixture source pressure. Concurrently, the pressure in the first beddecreases approaching atmospheric pressure. Before the secondary productmolecules have traversed the second bed, the concentration equalizationvalve 42 is opened allowing the primary product-enriched gas in thezeolite voids of the second bed to flow to the first bed. While theprimary product-enriched gas is flowing to the first bed, the cross-overvalving means is actuated. Actuating the cross-over valving meansdiscontinues the evacuation of the first bed and commences supplying thegaseous mixture and concurrently discontinues supplying the gaseousmixture to the second bed and commences evacuating it. Subsequent toactuating the cross-over valving means, the concentration equalizationvalve is closed terminating the pressure equalizing flow of the primaryproduct-enriched gas between the beds. The steps are cyclically repeatedto provide continuing fractionating of the primary product gas from themixture.

Referring again to FIG. 1, in a preferred embodiment the reservoir orproduct tank 30 maintains a reservoir of oxygen at a minimum pressure ofabout 14 psi. The oxygen-enriched gas contains from about 50 to about 99percent, desirably from about 70 to about 98 percent, and preferablyfrom about 84 to about 96 percent by volume of oxygen. In accordancewith conventional procedures, product tank 30 can be connected to apressure regulator (not shown) for controlling the pressure of theoxygen to a patient. Typically a pressure of 5 psi is utilized. A flowmeter (also not shown in FIG. 1) can be utilized to limit the flow rateto the patient such as from 0.1 to about 6 liters per minute with a flowrate of about 3 liters per minute often being utilized. If desired, ahumidifier (not shown) can add moisture to the oxygen-enriched gas. Thegas is delivered to the patient via tubing and breathing apparatus whichcan be inserted into the patient's nostrils.

In accordance with other concepts of the present invention,oxygen-enriched gas from an oxygen concentrator such as that describedhereinabove can be fed in any variety of methods to a compressor whereit is compressed to very high pressure and stored in a portable ormobile container such as a gas cylinder.

In the embodiment of FIG. 2, all of the oxygen-enriched gas is fed to acompressor. A concentrator (not shown but such as described hereinabove)has an oxygen-enriched product tank 30 wherein the pressure can vary asfrom about 14 to about 21 psi. The oxygen-enriched gas therein is fedvia line 201 to a flow meter 210 at the pressure of the concentratortank, that is from about 14 to about 21 psi. Flow meter 210 controls theflow rate of the oxygen-enriched gas which is fed via line 211 to buffertank 220 wherein the gas pressure therein can also range from about 14to about 21 psi. Via line 221, the predominantly oxygen gas is fed tocompressor 100. Compressor 100, in a manner described below, compressesthe oxygen-enriched gas to a pressure of about 2,250 psi and stores itwithin a mobile or portable cylinder 500. Depending upon the withdrawalrate of the oxygen-enriched gas by the compressor, the feed pressurethereto can range from 21 psi down to a predetermined cut-off pressuresuch as about 5 or 7 psi whereupon the compressor is automatically shutoff by a pressure sensor switch.

FIGS. 3 and 4 relate to embodiments wherein oxygen-enriched air fromproduct tank 30 of the oxygenator is fed by various methods desirably toa buffer tank of the compressor but prioritized as with regard to oxygenconcentration and/or a sufficient pressure. For example, the feed rateto a patient can vary from between 0.1 and 6 liters per minute at apressure of a predetermined value such as 5 psi with the remainingoxygen-enriched gas generally being fed at a different pressure to thebuffer tank. The buffer tank can generally contain a broad range ofpressure therein such as, for example, between 14 and 21 psi. However,as noted with regard to FIG. 2, depending upon the withdrawal rate ofthe gas in the buffer tank by the compressor, the pressure thereof candrop down to a predetermined cut-off pressure, such as 7 psi, which ishigher than the pressure of the gas being fed to the patient to ensurean adequate flow of the oxygen-enriched gas to the patient.

Referring to the embodiment of FIG. 3, a 5-psi regulator 210 emitsoxygen-enriched gas from product tank 30 into flow line 220 and feedsthe same to flow meter 230 which subsequently emits the oxygen-enrichedgas to the patient at a predetermined flow rate of from 0.1 to 6 litersper minute. Optionally, the flow meter can be closed so that all theenriched oxygen is directed to the compressor. Gas not directed to thepatient is carried via line 240 to two-way valve 250. A very smallportion of the gas in line 220 is directed through line 260 throughrestrictor 262 into oxygen sensor 265 which detects whether or not theconcentration of the oxygen is of a predetermined value such as is atleast 84 percent. When the oxygen sensor detects a concentration at orabove the predetermined level, two-way valve 250 is open and permits theoxygen-enriched gas to flow through line 270 into buffer tank 200wherein the pressure is essentially the same as the oxygen product tankpressure. However, should the oxygen sensor not detect a suitable oxygenconcentration, two-way valve 250 is closed so that the oxygenconcentrator can build up a sufficient oxygen concentration. Thisarrangement prioritizes the flow of oxygen-enriched gas so that thepatient is assured of receiving a gas having a minimum oxygenconcentration therein. Buffer tank 200 can have a regulator 280 thereongenerally set at 12 psi to admit the oxygen-enriched gas to thecompressor when needed. Alternatively, the pressure regulator can be setat anywhere from about 13 to about 21 psi. Restrictor 290 controls theflow rate of gas from the buffer tank to the compressor. Should thecompressor drop the pressure in the buffer tank to below a predeterminedvalue, a pressure sensor (not shown) will automatically cut off the flowof gas at a pressure above the pressure of the gas being fed to thepatient. This prioritization assures that the patient receives prioritywith regard to oxygen-enriched gas.

The embodiment of FIG. 4 emits the oxygen-enriched gas through a 14 toabout an 18-psi regulator 300 into flow line 305 having flow raterestrictor 307. The flow is then split with a portion via line 310 goingthrough 5-psi regulator 320 and into flow meter 330 which then directsthe gas to the patient at a desired flow rate of generally from 0.1 to 6liters per minute, although optionally the flow meter can be closed. Theremaining portion of the gas is directed via line 340 to two-way valve350. A small portion of the gas going to the patient is diverted throughline 365 through flow restrictor 367 to oxygen sensor 360. As in FIG. 3,the oxygen sensor is set at a predetermined value such as aconcentration of 84 percent so that when the level is not achieved,two-way valve 350 is closed through electrical line 355. This aspectallows the amount of oxygen in the concentrator tank to be increased bythe oxygenator unit. The same prioritizes the concentration of oxygen toensure that the patient receives an amount of oxygen of at least theminimum predetermined value. When the oxygen concentration issufficient, the gas flows through two-way valve 350 into line 370 andinto buffer tank 200 where it is stored generally at a pressure of about14 to 18 psi. A relief valve 385 which can be set at any desired valuesuch as about 14 psi ensures that gas under sufficient pressure is beingadmitted to the buffer tank. The oxygen-enriched gas is admitted to thecompressor via line 380. Should the compressor withdraw gas faster thanit is being received by the buffer tank, the pressure therein will drop.A pressure sensor switch (not shown) can be set to a predetermined value(e.g., about 7 psi) to ensure or prioritize that a sufficient amount orflow of gas is being fed to the patient. The predetermined shut-offpressure of the compressor is always above the pressure of the gas beingfed to the patient. The embodiment of FIG. 4 is preferred.

While the above description, as exemplified by FIGS. 2, 3, and 4,generally constitutes a preferred embodiment of the present invention,it is to be understood that the same can be modified. For example,oxygen product tank 30 need not be utilized. Instead, theoxygen-enriched air from an oxygen concentrator, such as shown in FIG.1, can be fed to the buffer tank via the shown and described flow linesof the various embodiments such as set forth in FIGS. 2, 3, and 4.Accordingly, the oxygen-enriched air will be separated with onecomponent directed to the patient and the other component being directedto the buffer tank. Prioritization of the oxygen enriched gas to thepatient either by a minimum oxygen concentration or a sufficientpressure in the buffer tank is still generally utilized. Alternatively,an enriched oxygen product tank 30 can be utilized and the buffer tankcan optionally be eliminated. In other words, enriched oxygen from theproduct tank can be fed via one component to the patient and to a secondcomponent via the flow line shown to the compressor. In this situation,prioritization of the desired flow and oxygen concentration to thepatient is maintained as described hereinabove with regard to either thelevel of oxygen concentration or an adequate pressure being admitted tothe compressor.

Referring now to the compressor assembly 100 as shown in FIGS. 7 and 8,it generally utilizes an AC electric-drive motor 105 which can rotate atany desired speed, e.g., 1,700 rpm. Motor 105 can contain a fan (notshown) either within the motor housing or immediately adjacent theretoto draw air through the motor to cool the same. Power is conveyed fromthe motor through shaft 106 to drive wheel 107. Desirably the drivewheel has a plurality of grooves therein to receive a V-belt such asmain drive belt 109. Such belts are generally reinforced with fiber andhave a very long life. Main drive belt 109 is connected to main gear 110which contains a plurality of grooves 113 therein. The number ofperipheral grooves 113, as well as the size and location thereof,coincides with the grooves of drive wheel 107 and matingly engage aplurality of projections located on main drive belt 109. Extending frommain gear 110 is an offset hub gear 114 which has a much smallerdiameter than main gear 110. Hub gear 114 also has grooves 115 thereonto receive a secondary drive V-belt 122. A second or secondary largegear 116 has grooves on the periphery thereof which matingly engage thesecondary drive V-belt 122. Offset hub 114 through the secondary V-drivebelt 122 contacts and serves to drive secondary gear 116 which in turnis connected to crankshaft 130.

Through the utilization of the two large gears 110 and 116, adouble-reduction is obtained such that the rotational speed ofcrankshaft 130 is a desirably low speed such as approximately 50 rpm.Both drive belts 109 and 122 desirably have a spring-loaded idler arm125 and 127, respectively, which applies a small amount of tension. Theactual pull tension of the first belt can be about 20 pounds, whereasthe tension on the second belt can be about 100 pounds.

The multi-stage compressor of the present invention can have any numberof pistons, but in the present embodiment has three. As shown in FIG. 8,two of the pistons, i.e., the first and third pistons, are located onthe same crankshaft lobe, whereas the second piston is located on adifferent lobe offset 180° from the first and third pistons. The reasonfor this is that pistons one and three will be drawing in air when thesecond piston is being compressed and vice versa Although not shown, acrankshaft can be utilized which contains three lobes thereon, eachoffset from one another by approximately 110° to 130°, e.g., about 120°,so as to minimize the torque resistance applied to the motor during thecompression stroke.

The compressor of the present invention has three pistons, i.e., piston#1 (131), piston #2 (133), and piston #3 (135). Each piston is containedwithin a separate cylinder and thus piston #1 is contained within thefirst cylinder (132), the second piston is contained the second cylinder(134), and the third piston is contained within the third cylinder(136). While the diameter of the head 140 of the first piston isapproximately equal to the diameter of the base portion of the piston asshown in FIGS. 8 and 9, the diameter of the head of piston #2 (133) issmaller than that of piston #1, and the diameter of the head of piston#3 (135) is smaller than the diameter of piston #2 (133). However, thebase of each piston 131B, 133B, and 135B is of the same size for reasonsset forth hereinbelow. In order to permit pistons #2 and #3 to operateproperly, each contains an annular sleeve 134S and 136S on the inside ofthe cylinder wall the internal diameter of which is approximately equalto the external diameter of piston heads #2 and #3 respectively.

Regardless of the size of the piston head, it has two rings as generallyindicated in FIG. 9. Inasmuch as the rings of all three piston heads aregenerally the same, only the first piston is shown in FIG. 9. The pistonhead has two annular grooves or recesses therein, that is top pistonannulus 141 and bottom annulus 144. The top annulus contains a U-shapedseal therein generally made out of a Teflon® alloy or other low-frictionmaterial. The seal contains a coil tension spring 143 therein whichforces the seal radially outward against the cylinder wall to preventcompressed air from leaking through the piston head between the pistonand the cylinder wall. To also ensure the maintenance of a good seal,seal 142 is U-shaped so that upon the build-up of pressure in thecylinder head, the compressed gas will communicate and enter into theseal and force the outer edge thereof radially outward against thecylinder wall. Piston head bottom annulus 144 contains a flat orvertical glide ring 145 which extends around the annulus and is alsoradially forced outwardly by a coil tension spring 146 located therein.The bottom glide ring 145 can be made out of a Teflon® alloy and servesas a piston glide ring.

Connecting rod 148 connects the piston head to piston base 150. Thepiston bases of all three pistons are the same diameter and accordinglyengage a mating cylinder of essentially the same diameter. The pistonbase contains an upper base annulus 151 and a lower base annulus 155,both of which have a glide ring therein similar to if not identical toglide ring 145 of piston head annulus 144. Thus, upper base annulus 151has a glide ring 152 therein which is forced radially outward by coilspring 153. Similarly, lower base annulus 155 has a glide ring 156therein which is radially forced out by coil spring 157. Although threeglide rings have been shown and described as being identical, they canbe different and use different material, and the like. Piston base 150contains bore 158 which extends laterally therethrough. Bore 158receives wrist pin 159. The wrist pin and coil spring both serve tomaintain glide ring 156 in a radially outward position so as to bearagainst the cylinder wall.

The two-part piston assembly of the present invention contains bottomconnecting rod 160 as shown in FIG. 10. The connecting rod contains atop bore 161 through which wrist pin 159 extends. Bottom bore 163 of theconnecting rod extends about and matingly engages an appropriate portionof the crankshaft. In order to permit rotation of connecting rod 160about the crankshaft 130, sealed portion 164 of the connecting rodcontains bearings therein.

The net result of the two-part piston ring assembly of the presentinvention is that bearing 164 of connecting rod 160 can freely rotatewith the crankshaft in a rotary or circular motion whereas top bore 161moves in only a linear or reciprocal motion allowing piston rod 148 withthe piston head and base thereon to move only in a linear reciprocatingdirection. The same thus prevents lateral forces from being applied tothe cylinder wall which often results in wear and can create anoval-shaped cylinder wall. The two-part piston ring assembly of thepresent invention thus promotes long life of the piston and cylinderwall.

Although each piston serves to compress the gas admitted therein to ahigher pressure, a desirable aspect of the present invention, as notedabove, is that each subsequent piston head has a smaller area. Forexample, piston #1 (131) can have a diameter of approximately 1¾ inches,whereas piston #2 has a diameter of approximately 1¼ inches, and piston#3 can have a diameter of approximately ½ inch, which can be thediameter of essentially piston rod 148. Desirably, the increase inpressure from each stage or piston is proportional to the others. Thecompression ratio of each piston can vary, but generally is the same.Although compression ratios of up to 10 can be utilized, the desirablepressure range is from approximately 6 to about 8.

Inasmuch as heat is built-up during compression of the oxygen-enrichedgas, the flow lines between the pistons can be extended so that they arelong enough to permit the heat of compression to be absorbed by ambientair and thus cool the enriched pressurized gas therein. As shown in FIG.8, cooling line 182 from the first piston to the second piston can be inthe form of an undulating path or the like and the same is true withregard to cooling line 184 between the second and third pistons.

The operation of the compressor portion of the apparatus is as follows.Electric motor 105 which operates independently of the compressorfeeding air to the molecular sieves in the oxygen concentrator portionof the apparatus, through drive belts 109 and 122, rotates crankshaft130 thereby causing piston #1, #2, and #3 (131, 133, 135) to reciprocateand compress air in their respective chambers. More specifically,enriched oxygen gas from the compressor buffer tank is fed to the firstpiston. Piston 131 contains an inlet check valve 172, which permits airto enter the cylinder head space above the piston, and outlet checkvalve 173, which permits the compressed gas to exit from the firstpiston. The check valves permit flow of the gas in one direction so thatonce the gas is admitted to the first piston, during the compressionstroke thereof it cannot be forced back out to the buffer tank.Similarly, once forced out of the first piston, outlet check valve 173prevents the gas from being sucked in during the intake stroke of thefirst piston. In a similar manner, second piston 133 has an inlet checkvalve 175 which permits the compressed air from piston #1 to be drawninto the head space above piston 133, but prevents it from being forcedback into the first piston. Outlet check valve 176 prevents the gascompressing the second piston from being drawn back into the piston onceit has been expelled therefrom. In a similar manner, the gas which hasbeen further compressed in piston #2 is fed into piston #3 (135) throughinlet check valve 178 where it is further compressed. The compressed gasis then fed through outlet check valve 179 into enriched oxygen gasstorage cylinder 500. Outlet check valve 179 thus prevents the highlycompressed stored gas in the cylinder from being admitted back into thethird piston.

During the operation of the compressor, the gas in portable cylinder 500which is initially at ambient pressure, is gradually built up to desiredpressure. One such suitable pressure is approximately 2,250 psi. Ofcourse, different cylinders can accept either higher or lower gaspressures and readily maintain the same. Rupture disk 180 is a safetyfeature designed to rupture at a pressure in excess of the desiredstorage pressure of the gas cylinder. Thus, in the present embodiment,such a pressure can be approximately 2,800 psi. Although not shown,rupture disks can also be provided in the flow lines from the exit ofthe first and second cylinders to prevent undue build-up in these lines.A pressure regulator 181 serves to emit the oxygen enriched gas at apressure of about 5 psi to a patient via a flow meter (not shown) at anydesired rate, such as from about 0.1 to about 6 liters per minute.

As previously noted, the buffer tank contains oxygen-enriched gas at apressure of generally from about 7 or 14 psi to about 21 psi. Thecompressor is designed to commence compression generally when thepressure in the tank is generally at a maximum until it drops to apredetermined pressure, e.g., 7 or 8 psi. In general, the pressure iselectrically controlled by various switches, sensors, relays and thelike. Briefly, a master ON/OFF switch emits power to compressor motor105 which in turn causes the crankshaft to rotate and compress air. Twopressure-sensitive switches exist: a low pressure sensor which detectspressure below a predetermined value, e.g., 7 to 12 psi, and a highpressure sensor which detects pressure above 2,250 psi. When the lowpressure sensor detects pressure below the predetermined level, it willturn off motor 105 through a relay switch. This allows oxygen inflowfrom the concentrator to be built-up in the buffer tank to a desiredpressure. The low pressure sensor is a solid-state relay. Should therelay fail, it will fail closed and allow the motor to continue to run.Accordingly, this relay switch is connected in series with the highpressure sensor mechanical relay switch which will shut the motor offwhen the pressure in the cylinder reaches approximately 2,250 psi.

FIGS. 5 and 6 show the electrical circuitry of the compressor. Power isfed to the compressor initially through the resettable breaker 600 andthen to power switch 610. When the power switch is pushed to the “ON”position, power passes to the motor start switch 620, the start relaycommon contacts 630, and also lights the power indicator 640. When startswitch is depressed, the start relay coil is energized which causes bothswitches of the relay to close.

One of these closed switches passes the power to high pressure switch650 which is normally closed when the output pressure of the compressoris under 2,250 psi. The output of the high pressure switch is fed backto the start relay coil to keep the coil energized without the startswitch being depressed, but will cut power to the coil when highpressure is reached. (This occurs when a tank has been filled.) Theoutput of the high pressure switch is also connected to the common oflow pressure switch 660. While the input pressure from the concentratoris above the predetermined value, e.g., 7 psi, the low pressure switchis closed and the normally closed contact has power. This power signalis fed to the drive contact of the solid-state relay which, in turn,allows the solid-state output to be “turned on.” The output of thehigh-pressure switch is also connected to the run indicator 670 whichthen lights up.

The second closed switch of the start relay is connected to the “input”of the solid-state relay. When the solid-state relay is turned on by thesignal from the low pressure switch, power is passed to motor 105 andits start capacitors through the solid-state output. A common line isconnected to the other side of the motor to complete the circuit. Anhour meter 690 is wired in parallel to the motor to monitor motor runtime.

When the above occurs, the motor beings to run and remains running untilone of two conditions occur. The first condition would be the inputpressure to the compressor falls below a predetermined value, e.g., 7psi. This will cause low pressure switch 660 to open and solid-staterelay 695 to turn off, which in turn shuts off motor 105. If the inputpressure to the compressor rises above a desired predetermined pressure,low pressure switch 660 will close and once again turn on thesolid-state relay and start the motor. This is a normal occurrence thatis dependent upon concentrator efficiency and may be repetitive.

The second condition that will shut off the motor occurs when an oxygentank has been filled. The output pressure will rise above 2,250 psi andtherefore cause high pressure switch 650 to open. This cuts the power tothe start relay coil which causes both switches to open and cuts thepower to both the input of the high pressure switch and the input to thesolid-state relay thereby shutting off the motor. To start the motorafter this condition is reached requires start switch 620 to bedepressed. If greater than 2,250 psi remains, the high pressure switchwill remain open and no signal will be fed back to the start relay coilto keep it energized therefore causing the motor to remain off. Whilethe high pressure switch is open, run indicator 670 remains off.

Any direct shorts between power and common or any condition that drawsmore than 8 amps of current will cause resettable breaker 600 to popopen.

As apparent from the above, the operation of compressor 100 iscompletely independent of the oxygen concentrator and utilization of gascompressed thereby as a power or energy source. In other words, thepressure accumulated in the oxygen concentrator is not utilized to driveor operate any pistons in the compression portion 100 of the apparatus.

A distinct advantage of the apparatus and method for formingoxygen-enriched gas and compression thereof according to the presentinvention is the creation of a mobile or portable source of gascontaining high purity oxygen. Patients who require oxygen-enriched gas,as from about 80 to about 98 percent, are no longer confined to thevicinity of an oxygen concentrator as for example a bed, home, hospital,or a wheelchair. Rather, the patient can carry the mobile gas cylinderin any convenient manner, such as in a backpack, and thus can take tripsvia wheelchair, an automobile, and even planes and trains. Dependingupon the pressure and size of the storage cylinder, the oxygen supplycan be anywhere from about 2 to about 24 hours or even longer.

An alternative compact compressor 700 is shown in FIGS. 11 through 15wherein the motor, drive wheels and drive belt assembly is similar tothat shown in FIGS. 7 and 8. Motor 701 contains a shaft 702 whichthrough first drive belt 703 is connected to first drive wheel 705having first drive shaft 708. The drive wheel contains a plurality ofgrooves and projections to receive drive belt 703, which respectivelyincludes corresponding projections and grooves. First drive shaft 708 isconnected to hub gear 710. In order to transfer power from hub gear 710to second drive wheel 715, second drive belt 713 is utilized which has aplurality of projections and grooves which engage, respectively, groovesand projections of second drive wheel 715. Second drive wheel 715 isconnected to second drive shaft 718.

Due to utilization of motor 701, which generally can be any conventionalelectric motor capable of rotating at any desirable speed, for example,at about 1,600 or 1,700 RPM, with drive wheel 705 having hub gear 710and second drive wheel 715 having second drive shaft 718, a doublereduction of the rotational speed of the motor is achieved. Thereduction ratio of the motor shaft speed to the first drive wheel orshaft 708 thereof and the reduction from the first drive shaft 708 tothe second drive wheel and shaft 718 thereof can be any desirable valuedepending upon the diameter of the various drive wheels and hub shafts.Desirably the first reduction is approximately a ratio of 6:1 so firstdrive shaft 708 rotates at about 265 to about 285 RPM. The reductionratio between the first drive shaft 708 or offset gear and the seconddrive shaft 718 is also approximately 6:1 so that the second drive shaftrotates at approximately 44 to about 48 RPM. Although not shown, bothdrive belts 703 and 713 can pass over spring loaded idler arms whichapply a small amount of tension thereto and ensures tension between thevarious connective shafts or drive wheels. Alternatively, a toothed beltgear drive, etc., can be utilized which engages teeth located on thevarious drive wheels and hubs.

The compact compressor assembly 700 can generally contain any number ofcompression stages such as cylinders and pistons but desirably containsthree as shown. The first piston desirably is a wobble piston which isconnected in series with two sequential cylindrical pistons forcompressing the oxygen enriched gas or other gas to a generallypredetermined pressure. Considering wobble piston assembly 730, as seenin FIGS. 11 and 14A, it contains wobble piston 732 having a relativelylarge diameter head 733 thereon, which is fixedly connected byconnecting rod 734 to base 735 having aperture 737 therein. The wobblepiston is operated by first drive shaft 708 by means of offset cam 721which has an offset shaft 722 extending therefrom. Offset shaft 722engages wobble base aperture 737 to reciprocate the wobble piston. Sincethere is no pivot point in the vicinity of wobble piston head 733, asshaft 708 rotates wobble piston 732 will reciprocate in a longitudinaldirection and at the same time wobble. That is, the top portion of thepiston head or face will longitudinally proceed or recede the centerpoint of the piston head due to offset cam shaft 722. The wobble pistonassembly will compress enriched oxygen received from product tank 30 orthe buffer tank 200 and compress it in piston cylinder 740 when receivedfrom cylinder manifold head 742.

The compact multi-stage compressor of the present invention can havemore than one wobble piston assembly, although one is preferred. It canalso have more than two cylinder piston assemblies, although two arepreferred. As shown in FIG. 11, the second and third piston assemblies750 and 770 are generally offset longitudinally aligned and operativelyconnected to second drive shaft 718 so that as the gas, such as enrichedoxygen, is being compressed in one cylinder, the gas in the othercylinder is being drawn therein. Second drive shaft 718 has an offsetcam 726 located at the end thereof which cam contains offset cam shaft727 to which both piston assemblies 750 and 770 are connected.

The structure of the second and third cylinder assemblies is generallyshown in FIGS. 11 and 13. Second piston assembly 750 contains pistonhead 753, which is pivotally connected through a wrist pin, not shown,to connecting rod 754. Base 755 of the connecting rod through anaperture is pivotally connected to offset drive shaft 727. The pistonreciprocates within second cylinder 760 which contains cylinder manifold762 to admit and release the oxygen or gas from the cylinder. Uponcompression of the oxygen or gas in the second cylinder, it istransferred to the third piston assembly 770 via line 787.

Similarly, third piston assembly 770 contains piston head 773, whichthrough a pivotal wrist pin, not shown, is connected to connecting rod774. Connecting rod base 775 has an aperture therein which pivots aboutoffset drive shaft 727. The piston assembly is contained within thirdcylinder 780. Cylinder manifold 782 receives enriched oxygen or gas viatransfer line 787 from the second cylinder and after compressionthereof; the compressed oxygen or gas is transferred by line 789 to ahigh-pressure storage container such as a bottle cylinder 820.

The piston rings of the second piston head 753 are shown in FIG. 14B,enlarged for clarification, and contain a first annulus 791 which hasU-shaped seal 792 therein. A tension coil spring 793 resides within theU portion of the seal and serves to force the seal radially outwardlyagainst the walls of the cylinder. The base of the seal 794 extendsradially outward to further effect a seal with the cylinder wall. Asecond annulus 796 contains a glide ring 797 therein which is forcedoutwardly against a cylinder wall by coil spring 798. The third pistonhead is similar to the second piston head but the two seals areseparated from each other by connecting rod 774 as seen in FIG. 14C.Thus, a first annulus 801 has a U-shaped seal 802 therein containingtension coil spring 803 which forces the seal radially outward againstthe piston wall. As in FIG. 14B, base 804 of the first seal extendsradially outward against the cylinder wall. Separated by connecting rod774, a second annulus 806 in the piston head contains glide ring 807which is forced radially outward against the cylinder wall by coiltension spring 808. The configuration of the seals of the second andthird pistons help maintain a tight seal during operation assuring thatcompression is not lost.

The compact and lightweight compressor assembly 700 can achieve anydesirable final pressure (e.g., from about 500 to about 3,000 PSI) suchas that required for a compressed gas container and especially acompressed oxygen enriched bottle for use by a patient. In theembodiment shown and described, a final pressure of approximately 2,000PSI is often preferred. Accordingly, wobble piston 732, while having ashort stroke but a large piston head, generally receives enriched oxygenfrom product tank 30 or buffer tank 200 through a restrictor at anydesired pressure such as about 10 PSI and compresses it to about 60 PSI.Desirably, there is an accumulator tank 785 between the first pistonassembly and the second piston assembly 750 to store up the compressedgas produced by the wobble piston inasmuch as it reciprocatesapproximately six times for every one reciprocation of the second andthird pistons. This tank can be a conventional tank such as acylindrical tank, or desirably it can be in the form of a long thick butwide hose 785. Compressed gas from the wobble piston assembly, which isoperated by first power source 705, is transferred to second cylindermanifold 762, where it is compressed by the second piston, operated bysecond drive shaft 718, to a pressure of approximately 400 PSI. Fromthere it is transferred via line 787 to the input of third cylindermanifold 782 whereupon it is compressed by the third piston, which alsois driven by second drive shaft 718, to a pressure of approximately2,000 PSI.

To achieve the desired increase in pressure, the diameter of eachsubsequent piston head is generally decreased. It is to be understoodthat generally any desirable head diameter can be utilized. In theembodiments of FIGS. 11 through 15, the diameter of the wobble piston isgenerally about 1.8 inches. The diameter of the second piston head canbe approximately 0.875 inches, whereas the diameter of the third pistonhead is approximately 0.25 inches. The second and third pistons can havea stroke of approximately 1.25 inches, whereas the wobble piston canhave a stroke of approximately 0.375 inch. The embodiment of FIG. 11through 15 also contain check valves, generally before and after eachcylinder, to prevent the oxygen enriched gas from being pushed backwardsinto the preceding cylinder or into the product or buffer tank.

An advantage of the compressor of FIGS. 11-15 is that it generally iscompact and small, approximately ⅓ the size of the embodiment of thecompressor shown in FIG. 8, and also approximately ⅓ the weigh thereof,so that it can weight only about 40 pounds. Due to the compactness ofthe alternative compressor, it can be mounted directly or on top of theoxygen concentrator or it can be made an integral part thereof.

Bottle cylinder or high pressure storage container 820, can generally beof any size and contain any pressure although the above noted pressureof approximately 2,000 PSI is desirable. A small bottle of approximately62 cubic inches can last a patient for approximately two hours. Thistime can be extended to approximately six hours when utilized inconjunction with a conserving device. A large tank of approximately 283cubic inches can generally last a patient for approximately eight hoursor approximately twenty-four hours when utilized with a conservingdevice.

Manifold block 810 is located between third piston assembly 770 andbottle 820. The manifold block contains pressure gauge 812 and a highpressure switch which, as explained herein below, turns off thecompressor once a predetermined pressure is achieved. The manifold alsocontains a ruptured disc, not shown, as a safety backup should thepressure to the bottle become too high. The manifold block also containsa bleed-off valve, not shown, which gradually releases the pressurebuilt up in compressor assembly 700 as well as line 789 so that a loudabrupt pressure release noise is not caused. Bottle 820 also contains aruptured disc thereon, not shown, which is set to rupture at a pressurehigher than that of the manifold rupture disc. The bottle can alsocontain a pressure gauge 822.

The compact compressor 700 can be utilized in the same manner as before,that is in association with an oxygenator and with various flow schemes,designs, etc., whether prioritized to insure that a patient receives arequired amount of the oxygen enriched gas, or not prioritized.Accordingly, the flow diagrams of FIGS. 2, 3 or 4, can be utilized butit is to be understood that generally any other flow system can also beutilized to route the enriched oxygen from product tank 30 eitherdirectly, or indirectly, etc., to the buffer tank and to compactcompressor 700.

An example of electrical circuitry which can be utilized to operatecompact compressor assembly 700 is shown in FIG. 15.

Mains power (line voltage) is supplied through a three conductorgrounded line cord. The hot side of the mains power is connected to aresettable thermal circuit breaker. The output lead of the circuitbreaker feeds the mains power on/off switch. The neutral side of themains power is supplied to one side of the High Pressure switch PRS2,Low Pressure switch PRS1, the “Run” light L1, hour meter HM1, and thecompressor motor M1.

With the power switch SW1 on, mains hot is supplied to one side of the“Full” light 12, the “Start” switch SW2, and the maintaining contact ofrelay K1. When the momentary contact “Start” switch SW2 is depressed,power is supplied to the relay K1 coil, one side of the “Run” light L1,the coil of motor relay K2 and the maintaining contact of the motorrelay K2. The High Pressure switch PRS2 supplies the neutral mainsreturn to the relay K1 coil if the cylinder pressure is below the fullpressure setpoint, latching relay K1 on.

If the Low Pressure switch PRS1 is activated by sensing pressure aboveits setpoint, K2 is energized, supplying power to the hour meter and thecompressor motor. The motor relay will cycle on and off by the lowpressure switch if the inlet pressure goes above or below the switchsetpoint.

If the cylinder reaches the High Pressure switch PRS2 setpoint, PRS2will activate, removing neutral power from the coil of latching relay K1and lighting the “Full” light L2. This will remove power from the K1coil, causing the latching and motor relays K1 and K2 to bede-energized, stopping the compressor motor and turning off the “Run”light L1.

While in accordance with the patent statutes the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto, but rather by the scope of the attached claims.

What is claimed is:
 1. An apparatus for compressing and storing anoxygen-enriched gas, comprising; an oxygen concentrator product tankhaving enriched oxygen therein, a motor driven compressor operativelyconnected to said oxygen concentrator product tank to receiveoxygen-enriched gas therefrom, said motor driven compressor operatedindependently of an oxygen concentrator power source and operated by apower source other than oxygen-enriched gas from said concentratorproduct tank, said motor driven compressor being capable of compressingsaid oxygen-enriched gas to a high pressure, said motor drivencompressor containing a plurality of pistons, wherein a first piston isdriven by a first drive shaft and a second piston is driven by a seconddrive shaft, and a high-pressure storage container operatively connectedto said motor driven compressor for portable storage of saidhigh-pressure oxygen-enriched gas, wherein said first piston is a wobblepiston and wherein said second piston is a non-wobble piston, whereinsaid wobble piston compresses said gas from a first pressure to a secondpressure and wherein said non-wobble piston compresses said gas fromsaid second pressure to a third pressure.
 2. An apparatus forcompressing and storing an oxygen-enriched gas according to claim 1,including a second non-wobble piston connected to said second driveshaft, wherein a piston head of said first non-wobble piston has an areawhich is smaller than a head area of said wobble piston, and wherein ahead area of said second non-wobble piston is smaller than the area ofsaid first non-wobble piston head.
 3. An apparatus for compressing andstoring an oxygen-enriched gas according to claim 2, wherein said firstand second non-wobble pistons are substantially longitudinally aligned.4. An apparatus for compressing and storing an oxygen-enriched gasaccording to claim 2, including a bleed-off valve located before saidhigh-pressure storage container.
 5. An apparatus for compressing andstoring an oxygen-enriched gas according to claim 2, including a buffertank, said buffer tank operatively connected to said oxygen concentratorproduct tank and to said motor driven compressor, wherein saidoxygen-enriched gas is prioritized by primarily being capable of beingfed to a person and secondarily any excess oxygen-enriched gas beingcapable of being fed to said buffer tank, said prioritization includinga determination of an oxygen concentration of said gas by an oxygensensor and a termination of said oxygen-enriched gas being fed to saidbuffer tank when said oxygen concentration is below a predeterminedlevel.
 6. An apparatus for compressing and storing an oxygen-enrichedgas according to claim 5, wherein said first and second non-wobblepistons are substantially longitudinally aligned, and wherein saidsecond drive shaft rotates at a slower rate than said first drive shaft.7. An apparatus for compressing and storing an oxygen-enriched gasaccording to claim 1, including a buffer tank, said buffer tankoperatively connected to said oxygen concentrator product tank and tosaid motor driven compressor, wherein said oxygen-enriched gas isprioritized by primarily being capable of being fed to a person andsecondarily any excess oxygen-enriched gas being capable of being fed tosaid buffer tank, said prioritization including a determination of anoxygen concentration of said gas by an oxygen sensor and a terminationof said oxygen-enriched gas being fed to said buffer tank when saidoxygen concentration is below a predetermined level.
 8. An apparatus forcollecting and storing or distributing an oxygen-enriched gas,comprising; an oxygen concentration device having an inlet whichreceives low pressure air and an outlet which provides a source ofoxygen-enriched gas at a relatively low pressure to an inlet of a firststorage vessel; a pressure control device which receives a firstcomponent of said low pressure oxygen-enriched gas and outputs saidoxygen-enriched gas at a reduced predetermined pressure for use by apatient; a buffer tank having an outlet and an inlet adapted to receivea second component of said oxygen-enriched gas at said low pressure fromsaid first storage vessel outlet; a second storage vessel having aninlet and an outlet; a motor driven compressor connected to said buffertank outlet which compresses said oxygen-enriched gas and outputsoxygen-enriched gas at a relatively high pressure to said inlet of saidsecond storage vessel, wherein said compressor contains at least onewobble piston for compressing said oxygen-enriched gas wherein saidmotor driven compressor is operated independently of a power source ofsaid oxygen concentration device; and prioritizing apparatus connectedbetween an outlet of said first storage vessel and said motor drivencompressor and which interrupts the flow of said second component ofoxygen-enriched gas to said motor driven compressor when the pressure ofsaid second component of oxygen-enriched gas falls below a preset amountto ensure that said first component is sufficient to ensure the outputof said oxygen-enriched gas from said pressure control device at saidreduced predetermined pressure.
 9. An apparatus according to claim 8,including said motor driven compressor having a plurality of pistons,including at least one wobble piston for compressing saidoxygen-enriched gas to a first pressure, and at least one non-wobblepiston for compressing said oxygen enriched gas from said first pressureto a second pressure.
 10. An apparatus according to claim 9, whereinsaid wobble piston is connected to a first drive shaft and wherein saidat least one non-wobble piston is connected to a second drive shaft. 11.An apparatus according to claim 10, including at least a secondnon-wobble piston for compressing said gas from said second pressure toa third pressure, and wherein said second non-wobble piston is connectedto said second drive shaft.
 12. An apparatus according to claim 11,wherein said first and second non-wobble pistons are substantiallylongitudinally aligned and wherein said second drive shaft rotates at aslower rate than said first drive shaft.
 13. An apparatus according toclaim 12, wherein a piston head of said first non-wobble piston has anarea which is smaller than a head area of said wobble piston, andwherein a head area of said second non-wobble piston is smaller than thearea of said first non-wobble piston head.
 14. An apparatus according toclaim 12, further comprising a valve element connected between theoutlet of said first storage vessel and said motor driven compressor,and an oxygen concentration detector operatively connected to said valveelement which monitors said first component of said low pressureoxygen-enriched gas and which operates said valve element to interrupt aflow of said second component of oxygen-enriched gas to said motordriven compressor when a concentration of said second component ofoxygen-enriched gas reaches a set limit.
 15. A method of providing aportable source of oxygen utilizing a home health care oxygenconcentrator having a patient flow line to deliver product gas from aproduct tank to a patient comprising the steps of: setting a minimumconcentration of oxygen for the product gas and measuring the oxygenconcentration of the product gas to establish that the minimum is met;setting a minimum delivery flow rate of said product gas to saidpatient; measuring the delivery flow rate to said patient, and if theminimum delivery flow rate and the minimum concentration are met,directing excess product gas to a compressor to compress said productgas, said compressor having at least a first compression stage and asecond compression stage wherein one of said first and secondcompression stages utilizes a wobble piston for compressing said productgas and the other utilizes non-wobble piston for compressing saidproduct gas, and delivering said compressed product gas to a portablestorage unit.
 16. A method according to claim 15, wherein an excessproduct gas is directed to said compressor only so long as both theminimum delivery flow rate and the minimum concentration of oxygen inthe product gas are met.
 17. A method according to claim 16, whereinsaid first compression stage precedes said second compression stage andutilizes said wobble piston.
 18. A method according to claim 17, whereinsaid second compression stage utilizes multiple non-wobble pistons. 19.A method as set forth in claim 15, wherein the buffer tank containsproduct gas at a pressure of from about 7 to about 14 psi and theportable storage unit includes compressed product gas at a pressure offrom about 500 to about 3,000 psi.
 20. A method as set forth in claim19, wherein said first stage compresses said product gas to a pressureof from about 10 to about 60 psi.
 21. A method as set forth in claim 15,wherein said delivery flow rate is from about 0.1 to 6 liters perminute.
 22. A method as set forth in claim 15, wherein said wobblepiston is connected to a first drive shaft and said non-wobble piston isconnected to a second drive shaft.